# Relationships

Introduction
Field Names
Defining Relationships
- Conditional Relationships
Default Serialization
Links
- Removing Links
Data
Meta

# Introduction

The relationships member on a resource object is a relationships object, as defined by the JSON:API specification. Members of the relationships object represent references from the resource object in which it is defined to other resource objects.

A relationship object must contain at least one of the following:

links
data
meta

# Field Names

As noted in the Attributes chapter, members on the relationships object share a common namespace with attribute members, and the resource object's type and id. In other words, a resource cannot have an attribute or relationship with the same name, nor can it have an attribute or relationship named type or id.

It is recommended that the field name case of relationships follows the same convention as a resource's attributes. In other words, if you are using camel-case for attributes, you should also use camel-case for relationships.

# Defining Relationships

Relationships are defined on resources by creating a relationship object via the relation method. To add relationships to your resource object, add them to the relationships method.

For example, a posts resource may have the following relationships:

namespace App\JsonApi\V1\Posts;

use LaravelJsonApi\Core\Resources\JsonApiResource;

class PostResource extends JsonApiResource
{

    /**
     * Get the resource's relationships.
     *
     * @param \Illuminate\Http\Request|null $request
     * @return iterable
     */
    public function relationships($request): iterable
    {
        return [
            $this->relation('author'),
            $this->relation('comments'),
            $this->relation('tags'),
        ];
    }

    // ...

}

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Note that there is no distinction between to-one relationships (author in this example) or to-many relationships (comments, tags). This is because here we are defining the JSON:API relationship object, and whether it is a to-one or to-many relation can be determined by the data member.

When calling the relation method, we provide the JSON:API field name as the first argument. The relationship object will assume that the relationship name on the model is the camel-case form of the field name. For example, if we were using dash-case for our field names, a field name of blog-tags would assume the model's relationship is called blogTags.

If the model relationship name is different from this convention, provide it as the second argument. For example, if our JSON:API field name was author but the relationship on the model was user, we would define our relation as follows:

$this->relation('author', 'user')

# Conditional Relationships

Just as with conditional attributes, you can also define conditional relationships. To do this, use the when() and mergeWhen() methods. For example:

public function relationships($request): iterable
{
    return [
        $this->relation('author'),
        $this->when($request->user()->isAdmin(), $this->relation('publishedBy')),
        $this->mergeWhen($request->user()->isOwner(), [
            $this->relation('foo'),
            $this->relation('bar'),
        ]),
    ];
}

# Default Serialization

By default, relationship objects are serialized with the links member, and will include the self and related links.

Given our posts example above, the resultant JSON:API relationships object will be:

{
  "author": {
    "links": {
      "self": "http://localhost/api/v1/posts/123/relationships/author",
      "related": "http://localhost/api/v1/posts/123/author"
    }
  },
  "comments": {
    "links": {
      "self": "http://localhost/api/v1/posts/123/relationships/comments",
      "related": "http://localhost/api/v1/posts/123/comments"
    }
  },
  "tags": {
    "links": {
      "self": "http://localhost/api/v1/posts/123/relationships/tags",
      "related": "http://localhost/api/v1/posts/123/tags"
    }
  }
}

The data member of each relationship object will only be included if the relationship data has been requested by the client using an Include Path (opens new window).

For example, if the client requested that the author and tags relationships were included, the resultant JSON:API relationships object would be:

{
  "author": {
    "data": {
      "type": "users",
      "id": "456"
    },
    "links": {
      "self": "http://localhost/api/v1/posts/123/relationships/author",
      "related": "http://localhost/api/v1/posts/123/author"
    }
  },
  "comments": {
    "links": {
      "self": "http://localhost/api/v1/posts/123/relationships/comments",
      "related": "http://localhost/api/v1/posts/123/comments"
    }
  },
  "tags": {
    "data": [
      {
        "type": "tags",
        "id": "1"
      },
      {
        "type": "tags",
        "id": "3"
      }
    ],
    "links": {
      "self": "http://localhost/api/v1/posts/123/relationships/tags",
      "related": "http://localhost/api/v1/posts/123/tags"
    }
  }
}

The rest of this chapter describes how to customise the relationship serialization.

# Links

The self and related links are automatically included in the serialized relationship object. The URL is calculated by appending the either /relationships/{FIELD-NAME} (for the self link) or /{FIELD-NAME} (for the related link) to the resource's self URL.

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The resource's self URL is calculated on the resource class, i.e. PostResource in our example. See the Links Chapter if you need to customise the URL.

The relationship's URL field name is obtained from the schema field. By default, we dash-case the field name when using it in URLs. You can override this on your schema if needed.

# Removing Links

If you do not want the relationship object to have a self link, use the withoutSelfLink method:

$this->relation('author')->withoutSelfLink()

Likewise, if you do not want the relationship object to have a related link, use the withoutRelatedLink method:

$this->relation('author')->withoutRelatedLink()

If you want to remove both the self and related links, you can use the withoutLinks method:

$this->relation('author')->withoutLinks()

# Data

By default, we only include the data member in the relationship object if the client has requested it via the Include Path (opens new window) query parameter. This is because the data member provides resource linkage in a JSON:API Compound Document. (opens new window) It allows a client to link together all of the included resource objects within the document. Therefore the data member is only required in a relationship object if the related resource will be in the top-level included member of the Compound Document.

If the data member is being serialized because of an include path, our schema classes will already have taken care of eager loading the related models, so that you do not get "N+1" query problems.

# Specifying Data

By default we return the value of the model relationship to calculate the data member of the relationship. If you need the data to be something else, use the withData method:

$this->relation('author')->withData($this->someOtherValue)

Typically you would probably want to defer the calculation of data, so that it is only calculated if it will be serialized in the relationship. To do this, provide a Closure to the withData method:

$this->relation('author')->withData(fn() => $this->someOtherValue)

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Relationship data may be omitted if the client has not requested it via an include path. Additionally, a relationship may not be serialized if a client requests Sparse Fieldsets (opens new window) and does not request the named relationship field.

When manually returning data, you need to return a value that our encoder can convert to a JSON:API resource identifier. For a to-one relationship, this means you need to return either a related model or null. For a to-many relation, you need to return an iterable of related models.

# Showing Eager Loaded Data

By default data will only be included if it was requested via an include path query parameter. However, you may want to include the data if the related model is eager loaded.

For example, on our posts resource the related author may have already been loaded during authorization (e.g. to check whether the related author is the current signed-in user).

In this scenario we can show the eager loaded data by using the showDataIfLoaded method:

$this->relation('author')->showDataIfLoaded()

Note that this will not include the related resource in the included member of the JSON:API document. The included resources are always determined by the include path query parameter.

# Always Including Data

If you would always like your relationship object to have the data member, use the alwaysShowData method:

$this->relation('author')->alwaysShowData()

Note that this will not include the related resource in the included member of the JSON:API document. The included resources are always determined by the include path query parameter.

WARNING

If you are using the alwaysShowData method, you will need to ensure that the relation is always eager loaded to avoid "N+1" database query problems. See the Eager Loading chapter for details.

# Meta

Relationship objects may also contain a meta member. This contains any non-standard meta-information about the relationship.

To add meta to the relationship object, use the withMeta method to provide an array:

$this->relation('author')->withMeta(['foo' => 'bar'])

If the meta needs to be calculated, it is best to provide a Closure so that the calculation is only incurred if the relationship is being serialized:

$this->relation('author')->withMeta(fn() => ['foo' => 'bar'])

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A relationship may not be serialized if a client requests Sparse Fieldsets (opens new window) and does not request the named relationship field.

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